1. Field of the Invention
This invention relates generally to the field of chemical reactions. More specifically, the invention relates to methods of making linear alkylbenzenes, that is, an alkyl aromatic compound wherein an atom of hydrogen in a benzene ring is substituted by a paraffin hydrocarbon chain, incorporating high shear mixing.
2. Background of the Invention
Alkylbenzenes have a wide range of technical uses. For instance alkylbenzenes with a number of carbon atoms in the side chain ranging between 8 and 16 are intermediates in the manufacture of sulfonated detergents. Alkylbenzene derivatives, such as alkyl benzene sulfonates, are among others, used in detergent and surfactant product applications. Environmental legislation requires that these products be biodegradable. Alkylbenzenes with a branched aliphatic chain are not decayed, departing from such with a linear chain, by aerobic bacteria and therefore tend to accumulate in water discharged from plants employing such detergents. It is well known that, to be biodegradable, it is important for the alkyl chain to be linear, i.e. with very little or no branching and low, if any, quaternary carbons. As such, linear alkylbenzenes have emerged as the dominant detergent intermediate since the early 1960s driven by the environmental need to produce biodegradable detergents.
The commercial development of linear alkylbenzenes has focused on the extraction of high purity linear paraffins derived from hydrotreated kerosene feedstock. Initially, these linear paraffins were dehydrogenated, at less than complete conversion, to linear internal mono-olefins. The dehydrogenation effluent, a mixture of olefins and paraffins, was used to alkylate benzene using hydrofluoric acid as the catalyst to produce linear alkylbenzenes. The conversion of the olefins to alkylbenzenes facilitated the separation of the unreacted linear paraffins by fractionation and their recycle to the dehydrogenation process. The resulting linear alkylbenzene product became the synthetic detergent intermediate for the production of linear alkylbenzene sulfonate, a major biodegradable synthetic surfactant. Linear alkylbenzene sulfonate remains the dominant workhorse surfactant but its position in North America and Western Europe is constantly challenged by detergent alcohol derivatives.
This detergent alkylate is formed by the reaction of an aromatic hydrocarbon with an olefinic hydrocarbon having from about 6 to 20 carbon atoms per molecule. A better quality detergent precursor normally results from the use of olefinic hydrocarbons having from 10-15 carbon atoms per molecule. In an embodiment, the alkylation reaction may be a Friedel-Crafts alkylation. Linear alkylbenzenes have been produced commercially via the following routes: 1) Dehydrogenation of n-paraffins to internal olefins followed by alkylation with benzene using a hydrofluoric acid (HF) catalyst; 2) Dehydrogenation of n-paraffins to internal olefins followed by alkylation with benzene using a fixed-bed of acidic, non-corrosive solid catalyst; 3) Chlorination of n-paraffins to form monochloroparaffins. The monochloroparaffins are subsequently alkylated with benzene in the presence of an aluminum chloride (AlCl3) catalyst; and 4) Chlorination of n-paraffins to form chlorinated paraffins. The chlorinated paraffins are subsequently dehydrochlorinated to olefins (both alpha and internal). These olefins subsequently undergo benzene alkylation in the presence of an aluminum chloride catalyst. The preferred aromatic hydrocarbon is benzene but other hydrocarbons including toluene, xylene and ethylbenzene may also be alkylated in the same manner.
The preparation of linear alkylbenzenes by the catalytic alkylation of benzene with n-olefins may occur in the presence of Lewis acid catalysts, such as aluminum chloride boron trifluoride, hydrofluoric acid, sulfuric acid, phosphoric anhydride etc. In industrial practice the two major catalysts for the alkylation of benzene with higher alpha or internal mono-olefins (C10-C16 detergent range olefins), are aluminum chloride and hydrofluoric acid. The HF-based process has become more prevalent than ones based on aluminum chloride. Alternatively, a mixture of n-olefins and chloroparaffins may be used as the alkylating agent of benzene, in the presence of aluminum chloride or aluminum in powder form as a catalyst.
The use of HF and AlCl3 catalysts presents many challenges. For example, aluminum chloride is difficult to separate after reaction and produces a large amount of waste effluent. The desirability of avoiding the use of potentially hazardous chemicals like HF has motivated the development of improved mechanisms for the production of alkylbenzenes. The advances in making linear alkylbenzenes have focused on catalyst development or different reaction pathways. Reactions which involve olefinic hydrocarbons and are catalyzed by hydrogen fluoride usually proceed at a very fast rate. To reduce the amount of olefin polymerization and to promote production of a mono-alkylated aromatic product, the reactants are normally subjected to vigorous mixing and agitation at the initial contacting of the olefinic reactant with the hydrogen fluoride and aromatic reactant. The desired result is a uniform dispersion and intimate contacting of hydrocarbon and hydrogen fluoride phases and the avoidance of the formation of localized high temperatures or high hydrogen fluoride concentrations. Nothing has dealt with improving the mixing and dispersion of the reactants for lowering reaction time or lowering reaction pressure and temperature.
Consequently, there is a need for accelerated methods for making linear alkylbenzenes by improving the mixing of olefins into the liquid benzene phase.